Project Summary Cutaneous leishmaniasis is a major neglected tropical disease that is associated with clinical manifestations ranging in severity from relatively benign lesions to chronic highly ulcerated lesions to metastatic disease. Optimally, drug treatment would eliminate the parasites, but drugs developed to date fail to induce sterile cure and are often woefully inefficient at controlling the disease. Our new data strongly suggests that optimal control of cutaneous leishmaniasis requires a response that not only effectively eliminates the parasite, but also reduces the potential for immunopathology. In a series of publications, we have outlined the role of CD8 cytolytic T cells in driving inflammation by upregulating the inflammasome and inducing the release of IL-1?. Thus, our studies indicate that an immunopathologic pathway involving the inflammasome and IL-1? production is a major driver of disease. We further found that blocking NLRP3 or IL-1? in experimental models of severe cutaneous leishmaniasis ameliorates pathology mediated by CTLs without blocking protective immune responses, suggesting that either would be excellent targets for host-directed immunotherapy that could be used in conjunction with conventional anti-parasitic treatments. However, significant gaps in our knowledge of this pathologic response remain. Here we will utilize a combination of in vitro and in vivo approaches that will identify the cells undergoing inflammasome activation, determine the proximal signals that activate NLRP3, and define the chemokines that maintain this chronic immunopathologic response. To accomplish this in Aim 1 we will determine which cells contribute to NLRP3 dependent pathology during cutaneous leishmaniasis disease progression by defining when inflammasomes are activated following infection, identifying the cells involved and determining which cells are required for disease-promoting inflammasome activation. In Aim 2 we will identify the triggers of NLRP3 inflammasome activation in cutaneous leishmaniasis. Finally, we found that the chemokines CCL3 and CCL4 are associated with treatment failure in patients, and therefore in Aim 3 we will determine if these chemokines drive the chronicity of cutaneous leishmania lesions by promoting CD8 T cell or regulatory T cell recruitment to leishmanial lesions. Our proposed experiments have clear translational significance since they are founded upon substantial data obtained from leishmaniasis patients and are designed to identify the essential cells and signals required for disease. Such information will allow for a more specific targeting of immunopathology in leishmaniasis and identify additional targets for host-directed therapies in this chronic infection. Finally, these studies will be of more general significance, as this pathologic pathway is not unique to cutaneous leishmaniasis.